Differential pressure sensor

ABSTRACT

In order to reduce hysteresis and other noise components included in the output signal characteristic of a differential pressure sensor, an elastic reaction member which operates together with a diaphragm provided in a chamber of the differential pressure sensor includes a contact portion which contacts the diaphragm, and a plurality of springs which are arranged symmetrically about the contact portion. Each of the springs is a plate shaped or linear shaped spring which is bent into the form of a letter C, U, J, or V, and has one of its ends fixed to a wall which defines the chamber, while its other end is connected to the contact portion. When the contact portion shifts together with the diaphragm, the deformations of the plurality of springs are mutually balanced, so that rotation and horizontal deviation of the contact portion with respect to the diaphragm is suppressed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application ofPCT/JP2008/050238 filed on Jan. 11, 2008, and claims priority to, andincorporates by reference, Japanese Patent Application No. 2007-019528filed on Jan. 30, 2007.

TECHNICAL FIELD

The present invention relates to a differential pressure sensor whichdetects the amount of displacement of a diaphragm which is disposedbetween two chambers, and outputs a pressure difference signal.

BACKGROUND ART

Differential pressure sensors which detect the amount of displacement ofa diaphragm which is disposed between two chambers, and output apressure difference signal, are, for example, disclosed in PatentCitations #1 and #2. The differential pressure sensor which is disclosedin Patent Citation #1 has a cantilevered plate spring one end of whichis fixed to a housing and the other end of which contacts the diaphragm,and the position of the point of contact between the cantilevered platespring and the diaphragm changes according to the pressure differencebetween the chambers, with an electrical signal having a level whichcorresponds to the position of this point of contact being outputted asa pressure difference signal. The cantilevered plate spring describedabove is formed in a shape which, as a whole, extends in a singledirection from its fixed end to its contact point with the diaphragm.

And, in the differential pressure sensor which is disclosed in PatentCitation #2, a piston is contacted against a diaphragm, this piston iselastically pushed in the direction of the diaphragm by a coil spring,and an electrical signal having a level which corresponds to theposition of this piston is outputted as a pressure difference signal. Inorder always to keep the coil spring in a dead straight form, the coilspring is inserted into a narrow tube.

-   Patent Citation #1: Japanese Laid-Open Patent Publication Showa    61-230037 (for example FIGS. 2 and 8);-   Patent Citation #2: Japanese Laid-Open Utility Model Publication    Heisei 4-113044.

DISCLOSURE OF INVENTION Technical Problem

A certain noise component may be included in the pressuredifference—output signal characteristic of the pressure differentialsignal which is outputted from this differential pressure sensor, andthis may constitute a hindrance to accurate pressure differentialdetection. In particular, in an application which attempts to detectminute pressure differences at high accuracy, this type of noisecomponent characteristic is required to be extremely low. One noisecomponent of this type is a hysteresis characteristic (a discrepancybetween the curve of change of the output signal level when the pressuredifference rises, and the curve of change of the output signal levelwhen the pressure difference drops). A principal cause of such ahysteresis characteristic noise component can be sliding frictionbetween the components or unnecessary deformation of the diaphragm,caused when the diaphragm moves.

For example, with the differential pressure sensor disclosed in PatentCitation #1, when the diaphragm moves, the cantilevered plate springrotates (tilts) around its fixed end as a center, so that the relativeposition of the cantilevered plate spring with respect to the diaphragmchanges (in other words, sliding takes place between the cantileveredplate spring and the diaphragm). Due to this, sliding friction occursbetween the cantilevered plate spring and the diaphragm. In addition tothis, the above described rotation of the cantilevered plate springchanges the relative angle between the cantilevered plate spring and thediaphragm, and thus changes the direction of the reaction force which isapplied to the diaphragm from the cantilevered plate spring. Due tothis, the diaphragm experiences a reaction force in a direction which isdifferent from the direction opposite to its direction of shifting, andtherefore useless deformation thereof takes place.

And, with the differential pressure sensor disclosed in Patent Citation#2, when the diaphragm moves, the coil spring is extended or compressed,and thus the coil spring contacts against the wall surface of the narrowtube which holds it, and sliding friction takes place between them.

Accordingly, an object of the present invention is to reduce the noisecomponent included in the output signal characteristic of a differentialpressure sensor.

Another object of the present invention is to reduce the slidingfriction between components when the diaphragm moves.

Yet another object of the present invention is to reduce uselessdeformation of the diaphragm when the diaphragm moves.

Technical Solution

According to one aspect of the present invention, a differentialpressure sensor comprises: a housing comprising a first wall whichdefines a first chamber and a second wall which defines a secondchamber; a diaphragm disposed within the housing between the firstchamber and the second chamber, and comprising a movable part which canbe moved along a certain shift axis upon receipt of a pressuredifference between the first chamber and the second chamber; an elasticreaction member which applies an elastic reaction force to the movablepart; and a transducer which outputs an electrical signal according tothe position of the movable part along said shift axis. The elasticreaction member comprises a contact portion which contacts the movablepart and is shiftable together with the movable part, and a plate shapedor linear spring comprising a loose end which is connected to thecontact portion, and a fixed end which is connected to the housing. Thespring comprises a first spring portion and a second spring portionwhich are connected in series between the loose end and the fixed end,with the first spring portion extending in a first direction from theloose end to a mutual connection point between the first spring portionand the second spring portion, and the second spring portion extendingin a second direction from the mutual connection point to the fixed end.And the first spring portion and the second spring portion are disposedso that the first direction and the second direction mutually subtend anobtuse angle upon a two dimensional coordinate plane which is orthogonalto the shift axis.

With this differential pressure sensor, the above described first andsecond spring portions which are comprised in the spring of the abovedescribed elastic reaction member are disposed in a directionalrelationship as described above. That is to say, the above describedfirst and second spring portions are disposed so that, upon the abovedescribed two dimensional coordinate plane, they extend in generallyopposite directions. In this specification, this type of constructionfor a spring which is employed is termed a “balanced construction of aspring”. By employing an elastic reaction member with this “balancedconstruction of a spring”, when the movable part of the diaphragm andthe contact portion of the elastic reaction member shift together, thefirst and the second spring portions rotate in mutually oppositedirections, so that their rotations mutually balance one another to someextent, and thereby rotation of the contact portion with respect to thediaphragm is suppressed. As a result, useless deformation of thediaphragm is suppressed, so that noise in the pressure differentialsignal which originates in deformation of the diaphragm is reduced, andaccordingly the accuracy of pressure differential detection is enhanced.

A typical example of a spring in which such a “balanced construction ofa spring” is employed is a plate shaped or linear spring which is shapedas a letter “C”, “U”, “V”, or “J”.

In a preferred embodiment, the length of said second spring portion isgreater than the length of the first spring portion. Due to this, itbecomes easier to enhance the resolution of pressure differencedetection, because the length of the stroke of the diaphragm is made tobe longer.

In a preferred embodiment, said elastic reaction member comprises aplurality of the springs, each of which has one of the loose ends whichis connected in common to the contact portion; and the plurality ofsprings are arranged so that the direction that each spring among theplurality of springs and the direction that at least one other springextends from the contact portion mutually subtend an obtuse angle uponthe two dimensional coordinate plane.

In this specification, this type of construction for the plurality ofsprings is termed a “balanced construction in which a plurality ofsprings are employed”. By employing an elastic reaction member with this“balanced construction in which a plurality of springs are employed”,when the movable part of the diaphragm and the contact portion of theelastic reaction member shift together, the plurality of spring portionsand the contact portions are caused to rotate and deviate horizontallyin mutually opposite directions, so that their rotations and horizontaldeviations mutually balance one another to some extent, and therebyrotation and horizontal deviation of the contact portion with respect tothe diaphragm is suppressed. As a result, useless sliding between thediaphragm and the elastic member is suppressed, so that the hysteresischaracteristic of the pressure difference signal which originates inthis sliding is reduced, and accordingly the accuracy of pressuredifferential detection is enhanced.

A typical example of a “balanced construction in which a plurality ofsprings are employed” is one in which the plurality of springs arearranged symmetrically with respect to the contact portion.

In a preferred embodiment, the elastic reaction member further comprisesa branch portion which is connected to the contact portion, and which isseparate from the spring; and the transducer is adapted to output theelectrical signal in correspondence to the position of the branchportion. By employing this type of structure, no impediment affects theaccuracy of detection, since the part such as the branch portion whichis attached for position detection by the transducer does not exert anysubstantial influence upon the elastic characteristics of the elasticreaction member. As a variant example, it would also be acceptable toprovide the branch portion described above to the spring describedabove.

In a preferred embodiment, the elastic reaction member is disposed inthe first chamber or in the second chamber; and the transducercomprises: a shift mass which is fitted to the branch portion within thefirst chamber or the second chamber; and a detection element disposedexterior to the first chamber and the second chamber, which detects theposition of the shift mass within the first chamber or the secondchamber through the first wall or the second wall in a non-contactmanner. If this type of structure is employed, then, since the detectionelement is disposed exterior to the chambers, accordingly thisdifferential pressure sensor can be applied even to an application inwhich the fluid which is introduced into the chambers is one whichdesirably should not come into direct contact with the detectionelement, such as for example oil or water.

And, according to a second aspect of the present invention, adifferential pressure sensor comprises: a housing comprising a firstwall which defines a first chamber and a second wall which defines asecond chamber; a diaphragm disposed within the housing between thefirst chamber and the second chamber, and comprising a movable partwhich can be moved along a certain shift axis upon receipt of a pressuredifference between the first chamber and the second chamber; an elasticreaction member which applies an elastic reaction force to said movablepart; and a transducer which outputs an electrical signal according tothe position of the movable part along the shift axis. The elasticreaction member comprises a contact portion which contacts the movablepart of the diaphragm and is shiftable together with the movable part,and a plurality of plate shaped or linear springs, each of whichcomprises a loose end which is connected in common to the contactportion, and a fixed end which is connected to the housing. And theplurality of springs are arranged so that the direction that each springamong the plurality of springs and the direction that at least one otherspring extend from the contact portion mutually subtend an obtuse angleupon a two dimensional coordinate plane which is orthogonal to the shiftaxis.

With this differential pressure sensor, the above described “balancedconstruction in which a plurality of springs are employed” is employedfor the elastic reaction member. With this “balanced construction inwhich a plurality of springs are employed”, useless sliding between thediaphragm and the elastic reaction member is suppressed, so that thehysteresis characteristic of the pressure differential signal whichoriginates in this sliding friction is reduced, and accordingly theaccuracy of pressure differential detection is enhanced.

ADVANTAGEOUS EFFECTS

According to the present invention, the noise component included in theoutput signal characteristic of the differential pressure sensor isreduced, and the accuracy of the pressure difference detection which itprovides is enhanced.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, several preferred embodiments of the present inventionwill be explained with reference to the drawings.

FIG. 1 is a sectional view of a differential pressure sensor accordingto a first embodiment of the present invention. And FIG. 2 is aperspective view of an elastic reaction member which is fitted to thisdifferential sensor according to this embodiment.

As shown in FIG. 1, this differential pressure sensor 100 has a housing102 which is made from a rigid material, and this housing 102 has afirst wall 106 which defines a first chamber 104 and a second wall 110which defines a second chamber 108. The first chamber 104 is a lowpressure chamber into which a fluid at a low pressure (for example,working oil of a oil pressure circuit at a low pressure) is introduced,while, by contrast, the second chamber 108 is a high pressure chamberinto which a fluid at a high pressure (for example, working oil of a oilpressure circuit at a high pressure) is introduced from an inletaperture 109. As one example of how this differential pressure sensor100 may be used, the housing 102 may be fitted directly to a testsubject (for example, some oil filter in a oil circuit), and fluids attwo different pressures within this test subject (for example, workingoil before it passes through a filter element within the oil filter, andafter it has passed through the filter element) may be introduced intothe chambers 104 and 108 respectively.

A diaphragm 112, which is substantially shaped as a circular plate, isdisposed between the low pressure chamber 104 and the high pressurechamber 108. This diaphragm 112 has a movable part 114 in its centralportion, and this movable part 114 can shift in the horizontal directionin FIG. 1 upon receipt of the pressure difference between the lowpressure chamber 104 and the high pressure chamber 108. Here, for theconvenience of explanation, an orthogonal X-Y-Z coordinate system 200 isdefined. According to this coordinate system 200, the movable part 114can be shifted along the X axis direction.

The material of the diaphragm 112 is typically a material which is veryflexible such as rubber, but a material which is only slightly flexible,such as a metal, will also be acceptable, provided that the constructionallows the movable part 114 to be movable. It is desirable for thediaphragm 112 to be able to support itself, in other words, for thediaphragm 112 not to be deformed by the action of gravity, even if theattitude of the differential pressure sensor 100 with respect to gravitychanges. At a head end portion thereof, the movable part 114 of thediaphragm 112 is provided with a ball 116 which is made of a materialwhich is resistant to wear, and this ball 116 projects from the head endportion of the movable part 114 towards the low pressure chamber 104.

An elastic reaction member 118 is disposed within the low pressurechamber 104, for applying an elastic reaction force to the movable part114 of the diaphragm 112 in the direction opposite to its shiftingdirection. As shown in FIG. 1 and FIG. 2, this elastic reaction member118 comprises a contact portion 120 and a spring 122. The spring 122 isa long and narrow plate spring which is, schematically, bent into theshape of a letter “C” or the shape of a letter “U” along the directionin which it is thinnest, and is connected at one end 122A thereof(hereinafter termed its “loose end”) to the contact portion 120, whilebeing fixed to the housing 102, for example by a bolt, at its other end122B (hereinafter termed its “fixed end”). It should be understood that,instead of using a plate spring as the spring 122, it would also beacceptable to use a linear spring. This spring 122 exerts its elasticreaction force towards the movable part 114 on the contact portion 120,so that its contact portion 120 is always continuously contacted againstthe ball 116 of the movable part 114 of the diaphragm 112.

As shown in FIG. 2, this elastic reaction member 118 further comprises abranch portion 124 which is connected to the contact portion 120, andwhich is different from the above described spring 122. A shift mass 126is fixed upon this branch portion 124, and this shift mass 126 is onecomponent of a transducer for generating an electrical pressuredifference signal which corresponds to the position of the contactportion 120 along the X axis, in other words to the amount ofdisplacement. As shown in FIG. 1, this shift mass 126 (a permanentmagnet) is located within the low pressure chamber 104 in theneighborhood of a thinned portion 106A of the first wall 106 which isparallel to the X axis. When the contact portion 120 shifts along the Xaxis together with the movable part 114, the shift mass 126 shiftsparallel to the inner surface of this thinned portion 106A of the firstwall 106. A non contact detection element 128, which is anothercomponent of the transducer, is located outside the low pressure chamber104, in the neighborhood of the thinned portion 106A of the first wall106. This non contact detection element 128 detects the position of theshift mass 126 (i.e. the permanent magnet) upon the branch portion 124along the X axis (to put it in another manner, the position of themovable part 114 of the diaphragm 112) through the first wall 106 in anon-contact manner, and generates a voltage signal (a pressuredifference signal) which has a voltage level corresponding to thisdetected position. It should be understood that, as a variant example,it would also be acceptable to provide a branch portion to which theshift mass 126 is fixed at some spot upon the spring 122.

The pressure difference signal which is outputted from the non contactdetection element 128 is outputted to the exterior of the differentialpressure sensor 100 via wiring 130. The level of this pressuredifference signal indicates the magnitude of the pressure differencebetween the chambers 104 and 108.

In this embodiment, for the transducer described above, a device isemployed which uses the non-contact detection principle of convertingmagnetic field intensity into a voltage signal by utilizing the Halleffect, and the shift mass 126 is implemented as a permanent magnetwhich generates a magnetic field, while the non-contact detectionelement 128 is implemented as a Hall IC. The Hall IC which is utilizedfor the non-contact detection element 128 senses the intensity of themagnetic field generated by the shift mass 126 permanent magnet, andoutputs a voltage signal having a voltage level which corresponds tothis intensity as a pressure difference signal. It would also beacceptable to employ, as the transducer described above, an elementwhich uses some other non-contact detection principle.

The non-contact detection element 128 such as a Hall IC is disposedexterior to the chambers 104 and 108. Due to this, even if, as apressurized fluid, a liquid such as working oil of a hydraulic circuitor working water of a water pressure circuit is introduced into thechambers 104 and 108, this liquid cannot exert any negative influenceupon the electric circuitry of the non-contact detection element 128,because it does not come into contact with the non-contact detectionelement 128. Accordingly, the differential pressure sensor 100 accordingto this embodiment can be used for detecting pressure differential, notonly in an air pressure circuit, but also in a liquid pressure circuitsuch as a hydraulic (oil pressure) circuit or a water pressure circuit.

Next, the construction of the elastic reaction member 118 describedabove, and in particular the construction of the spring 122 which isconnected to the contact portion 120, will be described in detail.

A construction which, in this specification, is termed a “balancedconstruction” is employed for the spring 122 of the elastic reactionmember 118. In other words, what is meant by this balanced constructionfor the spring 122 is that, when the spring 122 deforms by the movablepart 114 of the diaphragm 112 and the contact portion 120 of the elasticreaction member 118 shifting along the X axis, it is arranged tosuppress relative rotation (i.e. inclination) of the contact portion 120with respect to the movable part 114, due to the deformation of someportion of the spring 122 and the deformation of some other portionbalancing one another (i.e. performing mutual cancellation). Thisbalanced construction will now be explained below in concrete terms.

As shown in FIG. 2, between its loose end 122A and its fixed end 122B,the spring 122 has a first spring portion 122C and a second springportion 122D which are connected together in series. The first springportion 122C extends from the loose end 122A to the mutual connectionpoint 122E between the first and second spring portions 122C and 122D,in a direction shown by an arrow sign 202 (hereinafter termed the “firstdirection”). On the other hand, the second spring portion 122D extendsfrom the mutual connection point 122E to the fixed end 122B, in adirection shown by an arrow sign 204 (hereinafter termed the “seconddirection”). As shown in FIG. 3A, upon the coordinate plane (i.e. theY-Z plane) which is orthogonal to the shift axis of the movable part 114(in other words, to the X axis), the angle 206 which is subtendedbetween the first direction 202 and the second direction 204 is 180° (inother words, they are exactly opposite to one another). It should beunderstood that this angle 206 which is subtended between the firstdirection 202 and the second direction 204 upon the Y-Z plane need notnecessarily be 180°; it would also be acceptable for this angle to be anobtuse angle, as shown in FIG. 3B (in other words, these directions maybe generally in opposite directions). In this way, the balancedconstruction for the spring 122 is implemented by arranging the firstspring portion 122C and the second spring portion 122D so that they aregenerally in opposite directions.

FIG. 4 is a simplified side view of the elastic reaction member 118, forexplanation of the operation of the balanced construction of the spring122 described above.

As shown in FIG. 4, a case is considered in which a pressure from thediaphragm 112 acts upon the contact portion 120 in the X axis direction,as shown by the arrow sign 208. In this case, the spring 122 is deformedfrom the shape shown by the solid line to the shape shown by the singledotted broken line. Moreover, in this case, the second spring portion122D is rotationally shifted anti-clockwise from the fixed end 122B, asshown by the arrow sign 210. At the same time, the first spring portion122C is rotationally shifted clockwise from the mutual connection point122E, as shown by the arrow sign 212. Thus, in this manner, the firstspring portion 122C and the second spring portion 122D are rotated inmutually opposite directions. Accordingly, at the contact portion 120,the rotation of the first spring portion 122C and the rotation of thesecond spring portion 122D are balanced out (to some extent, even if notperfectly), and the relative rotation (i.e., inclination) of the contactportion 120 with respect to the diaphragm 112 is kept down to anextremely small value. To put this in another manner, the contactportion 120 can be shifted almost parallel to the X axis direction,while hardly rotating at all. As a result, by the contact portion 120thus being shifted while hardly rotating at all, the direction of thereaction force which is exerted by the contact portion 120 upon thediaphragm 112 is kept almost to the X axis direction, and therebyunnecessary deformation of the diaphragm 112 which originates inrotation or inclination of the contact portion 120 is prevented. And theresult of this is that the noise component which originates indeformation of the diaphragm 112, included in the pressuredifference—signal level characteristic of the pressure difference signaloutputted from the transducer, is reduced, so that the accuracy ofpressure difference detection is improved.

Various possible variant embodiments are possible for the balancedconstruction of the spring 122. FIG. 5 shows an elastic reaction member1182 which is employed in one variant embodiment of the balancedconstruction of the spring 122.

With the elastic reaction member 1182 shown in FIG. 5, the spring 122 isformed in the shape of a letter “J”, and thus the length of the secondspring portion 122D is greater than the length of the first springportion 122C. By contrast, with the elastic reaction member 118 shown inFIGS. 1 and 2, the spring 122 was formed in the shape of a letter “C” orin the shape of a letter “U”, and thus the lengths of the first springportion 122C and the second spring portion 122D were almost the same.With this letter “J” shape which is the shape of the spring 122 as shownin FIG. 5, it is easy to design the spring 122 so that the shiftdistance (i.e. the stroke length) in the X axis direction of the contactportion 120 becomes longer when a force of the same magnitude is exertedby the contact portion 120, as compared with the shape of a letter “C”or the shape of a letter “U” shown in FIGS. 1 and 2. If the strokelength of the contact portion 120 becomes longer, then the resolutionfor pressure difference detection is enhanced.

FIG. 6 shows an elastic reaction member 1184 which is employed inanother variant embodiment of the balanced construction of the spring122.

With the elastic reaction member 1184 shown in FIG. 6, overall, thespring 122 has the shape of a letter “V”, so that both the first spring122C and the second spring portion 122D have almost completely straightshapes. By contrast, with the elastic reaction member 118 shown in FIGS.1 and 2, or with the elastic reaction member 1182 shown in FIG. 5, thespring 122 was formed in the shape of a letter “C”, in the shape of aletter “U”, or in the shape of a letter “J”, and thus the first springportion 122C and the second spring portion 122D were both curved intoalmost circular arcs. Thus, irrespective of whether the concreteconstruction of the spring 122 of a balanced construction is the shapeof a letter “C”, the shape of a letter “U”, the shape of a letter “J”,or the shape of a letter “V”, it is possible to anticipate operation inwhich rotation of the contact portion 120 is suppressed, as explainedwith reference to FIG. 4.

FIG. 7 is a perspective view of an elastic reaction member 1186 which isemployed in yet another variant embodiment of the balanced constructionof the spring 122. And FIG. 8 is a side view of this elastic reactionmember 1186 for explanation of the operation of the balancedconstruction shown in FIG. 7.

With any of the elastic reaction members 118, 1182, and 1184 describedpreviously, the spring 122 is a plate spring which is bent in thedirection in which its thickness is thinner (to put it in anothermanner, it is bent in a direction of rotation about, as a center, anaxis which is orthogonal to the shift axis of the contact portion 120(the X axis)). By contrast, with the elastic reaction member 1186 shownin FIG. 7, the spring 122 is a plate spring which is bent in thedirection in which its thickness is greater (to put it in anothermanner, it is bent in a direction of rotation about, as a center, anaxis which is parallel to the shift axis of the contact portion 120 (theX axis)). However, with the elastic reaction member 1186 shown in FIG.7, the feature that the first spring portion 122C and the second springportion 122D are disposed in generally opposite directions is the sameas with the previously described elastic reaction members 118, 1182, and1184. The pressure in the X axis direction shown by the arrow sign 208acts from the diaphragm 112 (not shown in the figure) to the contactportion 120.

As shown in FIG. 8, when a pressure like that shown by the arrow sign208 acts upon the contact portion 120, then, as shown by the arrow sign210, the second spring portion 122D is rotated clockwise as seen fromthe fixed end 122B, and at the same time, the first spring portion 122Cis rotated anti-clockwise as seen from the mutual connection point 122E,as shown by the arrow sign 212. Accordingly (in particular when theshift distance in the pressing direction is small), the rotation of thefirst spring portion 122C and the rotation of the second spring portion122D are balanced out (to some extent, even if not perfectly), and therelative rotation of the contact portion 120 with respect to thediaphragm 112 (not shown in the figure) is kept low.

As described above, various types of variation are possible in theconcrete structure of the balanced construction of the spring which canbe employed as the elastic reaction member. Moreover, differentvariations are possible, even for where the elastic reaction member isdisposed within the housing. For example, in the example shown in FIG.1, the elastic reaction member 118 is disposed within the low pressurechamber 104. But, as a variant example, a design may also be employed inwhich the elastic reaction member is disposed within the high pressurechamber 108.

FIG. 9 is a sectional view of a differential pressure sensor accordingto a second embodiment of the present invention. And FIG. 10 is asectional view of this differential pressure sensor taken along linesA-A in FIG. 9. Moreover, FIG. 11 is a perspective view of an elasticreaction member which is installed to this differential pressure sensor.

As shown in FIGS. 9 through 11, the principal point of differencebetween this differential pressure sensor 300 according to the secondembodiment and the differential pressure sensor 100 according to thefirst embodiment shown in FIGS. 1 and 2 is the construction of theelastic reaction member. In other words, as most clearly shown in FIG.11, the elastic reaction member 302 which is installed in thisdifferential pressure sensor 300 according to the second embodiment hasa construction in which two springs 306 and 308 which have substantiallythe same construction, size, and elastic characteristic are bothconnected to a single common contact portion 304. These two springs 306and 308 are arranged so as to be symmetrical with respect to the contactportion 308 upon the coordinate plane (i.e. the Y-Z plane) which isorthogonal to the shift axis of the contact portion 304 (i.e. the Xaxis). As shown in FIG. 5, each of these springs 306 and 308 is a plateshaped or linear spring which is formed into the shape of a letter “J”(this might be the shape of a letter “C” or the shape of a letter “U” asshown in FIGS. 1 and 2, or the shape of a letter “V” as shown in FIG.6). The springs 306 and 308 are connected to the common contact portion304 by their respective loose ends 306A and 308A, and are fixed to thehousing 102 by their respective fixed ends 306B and 306A, for examplevia bolts. Moreover, separately from the two springs 306 and 308, abranch portion 312 to which a shift mass 126 is fixed is connected tothe contact portion 304. It should be understood that, as a variantexample, it would also be acceptable to provide a branch portion at somespot upon the spring 306 or the spring 308, with the shift mass 126being fixed thereto.

With the elastic reaction member 302 shown in FIG. 11, “balancedconstructions” of two types are employed. The “balanced construction” ofthe first type is a “balanced construction of a spring” of the typealready explained, in which the two springs 306 and 308 are employed. Inother words, with the spring 306, its first and second spring portions306C and 306D are arranged so as generally to extend in mutuallyopposite directions upon the Y-Z plane. And, with the spring 308 aswell, its first and second spring portions 308C and 308D are alsoarranged so as generally to extend in mutually opposite directions uponthe Y-Z plane. Accordingly, each of the springs 306 and 308 individuallyis able to exhibit the type of operation already explained withreference to FIG. 4. And, in addition to this, as a “balancedconstruction” of a second type, a “balanced construction in which aplurality of springs are combined” is employed. In other words, this“balanced construction in which a plurality of springs are combined” isimplemented as a construction in which the two springs 306 and 308 arearranged symmetrically in the Y-Z plane with respect to the contactportion 308. To put this in another manner, in this type of symmetricalconfiguration of the two springs 306 and 308, the angle subtended uponthe Y-Z plane by the directions 402 and 404 in which the two springs 306and 306 extend from the contact portion 304 (and in particular by thefirst spring portions 306C and 308C which are connected to that contactportion 304) is 180°. It should be understood that this angle which thedirections 402 and 404 of the two springs 306 and 308 subtend upon theY-Z plane need not necessarily be 180° (i.e. they need not extend inperfectly opposite directions); it may be an obtuse angle (in otherwords, they may extend in generally opposite directions).

FIG. 12 is a simplified side view of an elastic reaction member 302, forexplanation of the operation of the balanced construction describedabove, in which a plurality of springs (for example, two springs) arecombined.

As shown in FIG. 12, when a pressure from the diaphragm 112 (not shownin the figure) is applied to the contact portion 304 as shown by thearrow sign 208, then the two springs 306 and 308 are deformed from theirshape shown by the solid line to their shape shown by the single dottedbroken line. At this time, the portions 306C and 308C of the two springs306 and 308 which are connected to the contact portion 304 (i.e. theirfirst spring portions) are made to rotate in mutually oppositedirections as seen from their fixed ends 306B and 308B, as shown by thearrow signs 406 and 408, and these two rotations balance one another out(i.e. mutually cancel one another) (at least to some extent, even if notabsolutely perfectly), so that rotation of the contact portion 304 withrespect to the diaphragm 112 is suppressed. As a result, the contactportion 304 is substantially shifted in parallel in the direction of theX axis, as shown by the arrow sign 410.

Furthermore, not only is the rotation of the contact portion 304 withrespect to the diaphragm 112 suppressed, but also horizontal deviationof the contact portion 304 with respect to the diaphragm 112 (i.e.,shifting in a direction which is orthogonal to the X axis) issuppressed. In other words since, with only the “balanced constructionof a spring” already explained with reference to FIG. 4, a slighthorizontal deviation of the contact portion 120 takes place as shown bythe arrow sign 214 in FIG. 4, accordingly a slight amount of slidingfriction is engendered between the contact portion 120 and the diaphragm112. By contrast, according to a “balanced construction in which aplurality of springs are employed” as shown in FIG. 11, since it isarranged for the plurality of springs 306 and 308 to shift in mutuallyopposite directions orthogonally to the X axis, accordingly these twoshifts balance one another out (at least to some extent, even if notabsolutely perfectly), so that horizontal deviation of the contactportion 304 is suppressed, and thus sliding between the contact portion120 and the diaphragm 112 is suppressed. As a result, the slidingfriction between the contact portion 120 and the diaphragm 112 issuppressed, and the hysteresis characteristic of the pressure differencesignal which originates in this sliding friction is suppressed to anextremely small level, so that the accuracy of pressure differencedetection is enhanced.

Many further variations upon “a balanced construction in which aplurality of springs are combined” are possible. FIG. 13 shows anelastic reaction member 3022 which employs one variant embodiment ofsuch a balanced construction in which a plurality of springs arecombined.

As shown in FIG. 13, each of the two springs 306 and 308 is a platespring which is bent in the direction of its width, as shown in FIG. 7,into the shape of a letter “C”, “U”, “J”, or “V”. These two springs 306and 308 are both connected to a common contact portion 304, and arearranged in directions which mutually subtend an obtuse angle upon theY-Z plane (for example, symmetrically with respect to the contactportion 304).

FIG. 14 shows an elastic reaction member 3024 which is employed inanother variant embodiment of this balanced construction in which aplurality of springs are combined.

With this elastic reaction member 3024 shown in FIG. 14, a “balancedconstruction of a spring” such as already explained is not employed foreach of the two springs 306 and 308. However, the first spring portions306C and 308C are both connected to a common contact portion 304, andare arranged in directions which mutually subtend an obtuse angle uponthe Y-Z plane (for example, symmetrically with respect to the contactportion 304). In this manner, even if only a “balanced construction inwhich a plurality of springs are employed” is used, but not a “balancedconstruction of a spring”, still an operation such as that explainedwith reference to FIG. 12 may be obtained.

FIG. 15 shows an elastic reaction member 3026 which is employed in yetanother variant embodiment of this balanced construction in which aplurality of springs are combined.

With the elastic reaction member 3026 shown in FIG. 15, three springs306, 308, and 310 are all connected to a common contact portion 304 (andare, for example, arranged symmetrically with respect to that contactportion 304). When the contact portion 304 shifts along the X axis, therotations and the horizontal deviations are balanced between these threesprings 306, 308, and 310, and thus the contact portion 304substantially shifts in parallel along the X axis.

As yet another variant example, which is not illustrated by any figure,it would also be possible to employ a balanced construction in whichfour or more springs were combined. In other words, these four or moresprings would be connected to a single common contact portion, and, foreach of these springs, at least one other spring would be arranged in adirection which mutually subtends an obtuse angle therewith upon the Y-Zplane (for example, would be arranged symmetrically thereto with respectto the contact portion 304). It would be acceptable to employ a“balanced construction of a spring” for each of these springs, oralternatively it would also be acceptable not to employ any suchconstruction.

Although several preferred embodiments of the present invention havebeen explained above, the scope of the present invention is not to beconsidered as being limited only to those described embodiments; thepresent invention may be implemented in various other manners, providedthat its gist is not departed from.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a differential pressure sensor accordingto a first embodiment of the present invention;

FIG. 2 is a perspective view of an elastic reaction member which isfitted to this differential sensor according to the first embodiment;

FIG. 3 is a figure for explanation of a balanced construction for aspring, which is implemented by disposing a first and a second springportion in generally opposite directions;

FIG. 4 is a side view of the elastic reaction member, for explanation ofthe operation of this balanced construction of the spring;

FIG. 5 is a side view of an elastic reaction member, for explanation ofa variant embodiment of a balanced construction of a spring;

FIG. 6 is a side view of an elastic reaction member, for explanation ofanother variant embodiment of a balanced construction of a spring;

FIG. 7 is a perspective view of an elastic reaction member which isemployed in another variant embodiment of a balanced construction of aspring;

FIG. 8 is a side view of an elastic reaction member 1186, forexplanation of the operation of the balanced construction shown in FIG.6;

FIG. 9 is a sectional view of a differential pressure sensor accordingto a second embodiment of the present invention;

FIG. 10 is a sectional view of this differential pressure sensoraccording to the second embodiment, taken along lines A-A in FIG. 9;

FIG. 11 is a perspective view of an elastic reaction member which isinstalled in this differential pressure sensor according to the secondembodiment;

FIG. 12 is an abbreviated side view of the elastic reaction member, forexplanation of the operation of this balanced construction in which aplurality of springs are combined;

FIG. 13 is a perspective view of an elastic reaction member which isemployed in one variant embodiment of this balanced construction inwhich a plurality of springs are combined;

FIG. 14 is a side view of an elastic reaction member which is employedin another variant embodiment of this balanced construction in which aplurality of springs are combined; and

FIG. 15 is a side view of an elastic reaction member which is employedin yet another variant embodiment of this balanced construction in whicha plurality of springs are combined.

1. A differential pressure sensor, comprising: a housing comprising afirst wall which defines a first chamber and a second wall which definesa second chamber; a diaphragm disposed within said housing between saidfirst chamber and said second chamber, and comprising a movable partwhich can be moved along a certain shift axis (X) upon receipt of apressure difference between said first chamber and said second chamber;an elastic reaction member which applies an elastic reaction force tosaid movable part; and a transducer which outputs an electrical signalaccording to a position of said movable part along said shift axis;wherein: said elastic reaction member comprises: a contact portion whichcontacts said movable part and is shiftable together with said movablepart; and a plate shaped or linear spring comprising a loose end whichis connected to said contact portion, and a fixed end which is connectedto said housing; said spring comprises a first spring portion and asecond spring portion which are connected in series between said looseend and said fixed end, with said first spring portion extending in afirst direction from said loose end to a mutual connection point betweensaid first spring portion and said second spring portion, and saidsecond spring portion extending in a second direction from said mutualconnection point to said fixed end; and said first spring portion andsaid second spring portion are disposed so that said first direction andsaid second direction mutually subtend an obtuse angle upon a twodimensional coordinate plane (Y-Z) which is orthogonal to said shiftaxis; and a length of said second spring portion is greater than alength of said first spring portion.
 2. A differential pressure sensoraccording to claim 1, wherein said spring is formed in a shape of aletter “C”, “U”, “V”, or “J”.
 3. A differential pressure sensoraccording to claim 1, wherein: said elastic reaction member comprises aplurality of said springs, each of which has one of said loose endswhich is connected in common to said contact portion; and said pluralityof springs are arranged so that a direction that each spring among saidplurality of springs extends and a direction that at least one otherspring extends from said contact portion mutually subtend an obtuseangle upon said two dimensional coordinate plane.
 4. A differentialpressure sensor according to claim 3, wherein said plurality of springsare arranged symmetrically with respect to said contact portion.
 5. Adifferential pressure sensor comprising: a housing comprising a firstwall which defines a first chamber and a second wall which defines asecond chamber; a diaphragm disposed within said housing between saidfirst chamber and said second chamber, and comprising a movable partwhich can be moved along a certain shift axis (X) upon receipt of apressure difference between said first chamber and said second chamber;an elastic reaction member which applies an elastic reaction force tosaid movable part; and a transducer which outputs an electrical signalaccording to a position of said movable part along said shift axis;wherein: said elastic reaction member comprises: a contact portion whichcontacts said movable part and is shiftable together with said movablepart; and a plate shaped or linear spring comprising a loose end whichis connected to said contact portion, and a fixed end which is connectedto said housing; said spring comprises a first spring portion and asecond spring portion which are connected in series between said looseend and said fixed end, with said first spring portion extending in afirst direction from said loose end to a mutual connection point betweensaid first spring portion and said second spring portion, and saidsecond spring portion extending in a second direction from said mutualconnection point to said fixed end; said first spring portion and saidsecond spring portion are disposed so that said first direction and saidsecond direction mutually subtend an obtuse angle upon a two dimensionalcoordinate plane (Y-Z) which is orthogonal to said shift axis; saidelastic reaction member comprises a plurality of said springs, each ofwhich has one of said loose ends which is connected in common to saidcontact portion; and said plurality of springs are arranged so that adirection that each spring among said plurality of springs extends and adirection that at least one other spring extends from said contactportion, mutually subtend an obtuse angle upon said two dimensionalcoordinate plane, and so that said contact portion can shift almostparallel to itself without rotation.
 6. A differential pressure sensoraccording to claim 1, wherein: said elastic reaction member furthercomprises a branch portion which is connected to said contact portion,and which is separate from said spring; and said transducer is adaptedto output said electrical signal in correspondence to a position of saidbranch portion.
 7. A differential pressure sensor according to claim 6,wherein: said elastic reaction member is disposed in said first chamberor in said second chamber; and said transducer comprises: a shift masswhich is fitted to said branch portion within said first chamber or saidsecond chamber; and a detection element disposed exterior to said firstchamber and said second chamber, which detects a position of said shiftmass within said first chamber or said second chamber through said firstwall or said second wall in a non-contact manner.
 8. A differentialpressure sensor according to claim 1, wherein said spring comprises abranch portion, and a portion of said transducer is fixed upon saidbranch portion.
 9. A differential pressure sensor according to claim 3,wherein: said first chamber is a low pressure chamber, and said secondchamber is a high pressure chamber; said elastic reaction member isdisposed within said low pressure chamber; said elastic reaction memberfurther comprises a branch portion, separate from said springs, which isconnected to said contact portion; said transducer comprises: a shiftmass which is fitted to said branch portion; and a detection elementdisposed exterior to said low pressure chamber and said high pressurechamber, which detects a position of said shift mass through a wall ofsaid low pressure chamber in a non-contact manner; each of saidplurality of springs is formed in a shape of a letter “C”, “U”, “V”, or“J”; each of said plurality of springs comprises a first spring portionand a second spring portion which are connected together in seriesbetween said loose end thereof and said fixed end thereof; said firstspring portion extends in a first direction from said loose end to amutual connection point between said first and second spring portions;said second spring portion extends in a second direction from saidmutual connection point to said fixed end; and a length of said secondspring portion is greater than a length of said first spring portion;and said plurality of springs are arranged symmetrically with respect tosaid contact portion.
 10. A differential pressure sensor according toclaim 2, wherein: said elastic reaction member further comprises abranch portion which is connected to said contact portion, and which isseparate from said spring; and said transducer is adapted to output saidelectrical signal in correspondence to a position of said branchportion.
 11. A differential pressure sensor according claim 2, whereinsaid spring comprises a branch portion, and a portion of said transduceris fixed upon said branch portion.
 12. A differential pressure sensoraccording to claim 3, wherein: said elastic reaction member furthercomprises a branch portion which is connected to said contact portion,and which is separate from said spring; and said transducer is adaptedto output said electrical signal in correspondence to a position of saidbranch portion.
 13. A differential pressure sensor according claim 3,wherein said spring comprises a branch portion, and a portion of saidtransducer is fixed upon said branch portion.
 14. A differentialpressure sensor according to claim 4, wherein: said elastic reactionmember further comprises a branch portion which is connected to saidcontact portion, and which is separate from said spring; and saidtransducer is adapted to output said electrical signal in correspondenceto a position of said branch portion.
 15. A differential pressure sensoraccording claim 4, wherein said spring comprises a branch portion, and aportion of said transducer is fixed upon said branch portion.
 16. Adifferential pressure sensor according to claim 5, wherein: said elasticreaction member further comprises a branch portion which is connected tosaid contact portion, and which is separate from said spring; and saidtransducer is adapted to output said electrical signal in correspondenceto a position of said branch portion.
 17. A differential pressure sensoraccording claim 5, wherein said spring comprises a branch portion, and aportion of said transducer is fixed upon said branch portion.
 18. Adifferential pressure sensor according to claim 10, wherein: saidelastic reaction member is disposed in said first chamber or in saidsecond chamber; and said transducer comprises: a shift mass which isfitted to said branch portion within said first chamber or said secondchamber; and a detection element disposed exterior to said first chamberand said second chamber, which detects a position of said shift masswithin said first chamber or said second chamber through said first wallor said second wall in a non-contact manner.
 19. A differential pressuresensor according to claim 12, wherein: said elastic reaction member isdisposed in said first chamber or in said second chamber; and saidtransducer comprises: a shift mass which is fitted to said branchportion within said first chamber or said second chamber; and adetection element disposed exterior to said first chamber and saidsecond chamber, which detects a position of said shift mass within saidfirst chamber or said second chamber through said first wall or saidsecond wall in a non-contact manner.
 20. A differential pressure sensoraccording to claim 14, wherein: said elastic reaction member is disposedin said first chamber or in said second chamber; and said transducercomprises: a shift mass which is fitted to said branch portion withinsaid first chamber or said second chamber; and a detection elementdisposed exterior to said first chamber and said second chamber, whichdetects a position of said shift mass within said first chamber or saidsecond chamber through said first wall or said second wall in anon-contact manner.